Sedimentary Facies of the Longmaxi Formation Shale Gas Reservoir in the Weiyuan Area Based on Elemental Characteristics

Table 1

Classification of the sedimentary microfacies of the Longmaxi Fm.

Sedimentary facies	Subfacies	Microfacies	U/Th	TOC (%)	SiBio (%)
Shelf	Inner shelf	Shallow-water argillaceous silty shelf	<0.15	<1.5	<2.0
		Shallow-water silty argillaceous shelf	0.15~0.5	1.5~2.0	<2.0
	Outer shelf	Deep-water silty argillaceous shelf	0.5~1.25	2.0~3.0	10.0~15.0
		Organic-rich silty argillaceous shelf	0.5~1.25	3.0~5.0	10.0~15.0
		Organic-rich silicon-containing argillaceous shelf	1.25~2.0	3.0~5.0	15.0~20.0
		Organic-rich siliceous argillaceous shelf	>2.0	>5.0	>20.0